Abstract

Fibroblast Growth Factor-23 (FGF-23) accumulates in blood of patients with chronic kidney disease (CKD) and is associated both with cardiovascular complications and disease progression. However, our knowledge of the sites and mechanisms which regulate plasma FGF-23 is still incomplete. We measured plasma intact FGF-23 across the kidney, splanchnic organs and lung in eleven patients (eGFR 60 ± 6 ml/min) during elective diagnostic cardiac catheterizations. In these patients FGF-23 was removed by the kidney, with a fractional extraction (FE) of ~22%. The FE of FGF-23 across the kidney was similar to that of creatinine (~17 %, p=NS). In addition, the FGF-23 FE by the kidney was significantly directly related to eGFR (r = 0.709 p = 0.018) and to kidney creatinine FE (r=0.736 p=0.013) but only as a trend, to plasma phosphate levels (r=0.55, p=0.18). There was no difference in FGF-23 levels in blood perfusing splanchnic organs and cardiopulmonary bed. However, the arterial-venous difference of FGF-23 across the lung was directly related to FGF-23 pulmonary artery levels, suggesting that the lung, and possibly the heart, participate in the homeostasis of plasma FGF-23 when its systemic levels are increased.
Our data show that the human kidney is the only site for FGF-23 removal from blood and suggest that FGF-23 is predominantly removed by glomerular filtration. The kidney ability to remove FGF-23 from the circulation likely accounts for the early increase in blood of FGF-23 in patients with CKD.